The aim of this work is to derive precise formulas which describe how the
properties of subwavelength devices are changed by the introduction of errors
and imperfections. As a demonstrative example, we study a class of
cochlea-inspired rainbow sensors. These are devices based on a graded array of
subwavelength resonators which have been designed to mimic the frequency
separation performed by the cochlea. We show that the device's properties
(including its role as a signal filtering device) are stable with respect to
small imperfections in the positions and sizes of the resonators. Additionally,
if the number of resonators is sufficiently large, then the device's properties
are stable under the removal of a resonator.